On occasion there is a need to inject fuel into high temperature supersonic air flow. There is a need to retract the fuel injectors when they are not in use to avoid overheating and therefore one must be able to insert and retract the fuel nozzles.
The fuel is introduced simultaneously at a plurality of closely spaced locations. Therefore a plurality of injectors are joined in a header system in the form of a rake. Because of the differential thermal expansion between the wall containing the supersonic air flow and the header system, each injector must be able to move parallel to the surface of the wall through which it passes as well as in and out of the wall. It must at the same time seal against egress or leakage of hot gas from the gas flow path.